David Maidment

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Total Maximum Daily Load for Zinc in Nueces Bay

• David Maidment Lynn E. Katz Imane Mrini
• Center for Research in Water Resources
• The University of Texas at Austin

Project Managers Sandra Alvarado - TCEQ Blake
Traudt - GLO
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Zinc Impairment / criteria

• Texas Department of Health Guidelines
• Average zinc concentrations in oysters from
  Nueces Bay should be consistently below 700 mg
  Zn/kg edible tissue
• Data Observations
• High concentrations ( 2,389 mg/kg) were found in
  oysters resulting in acute adverse health effects
  (TDH, 1994)
• No threat for fish or crabs

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Zinc in Oyster Tissue
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Outline

• Review of issues
• Study area Nueces Bay
• Zinc impairment
• Study objectives
• Study of Zinc monitoring data
• Estimation of watershed zinc loadings
• Next steps

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Sources of Contamination
?
?
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Water Quality Pollution Loading Model
Load Mass/Time Runoff Vol/Time x
Concentration Mass/Vol
Precip.
Runoff
DEM
LandUse
Accumulated Load
EMC Table
Load
Concentration
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Expected Mean Concentration
Land Use
EMC
Table derived from USGS water quality monitoring
sites
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Water Quality Analysis
Salinity Concentration and Mass Fluxes in
Corpus Christi Bay.
Finite Segment Analysis
Flow of water
Transport of Constituents
Fluxes
Loads
Advection
Dispersion
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Observed vs. Expected
Zinc (µg/l)
Chromium (µg/l)
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Physicochemical Reactions
sunlight
Atmospheric Deposition
Photochemical Reactions
Inorganic Reactions
Flux
Organic/Biological Reactions
Flux
Sediment-Water Exchange
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Resuspension and Deposition
Deposition
Resuspension
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Study Area Nueces Bay

• Nueces bay TMDL segment 2482
• Average area of 74.87 Km2 Mean depth 0.68 to
  0.92m
• Relatively small average residence time (V/Q)
  30 days
• Uses Aquatic life, contact recreation, fishing,
  production of edible oysters, clams and mussels,
  and shellfish harvesting (oyster water use )
• TMDL for zinc in oyster tissue

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Study Objectives

• Acquire existing data and information necessary
  to support modeling and assessment activities
• Determine current allowable loadings of the
  constituent (zinc)
• Allocate the total loadings to appropriate
  pollutant sources

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Zinc Monitoring Stations
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Zinc Monitoring dataZinc in sediments
Zn conc. ( ppm)
71 - 140
140.1 - 430
430.1 - 864
864.1 - 2100
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Zinc Monitoring dataZinc in water
Zinc conc. ( ?g/L)
15 - 21
21.1 - 40
40.1 - 53.4
53.5 - 73.3
73.31 - 546
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Zinc Monitoring dataZinc in sediments vs zinc
in water
Water
Sediment
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Hydrodynamic Circulation
Simulation by Dr Junji Matsumoto, TWDB
Animation
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Sediment Data for Nueces Bay
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Sediment Data for the Inner Harbor
Average Zinc Conc. 440 ppm
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Zinc Monitoring dataZinc partitioning in
sediment/water/oyster tissue
Ratio 2300
Ratio 55,000
Ratio 24
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Watershed delineation Procedure
procedure developed for delineating watersheds in
coastal and low-lying regions with little to no
slope.
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Watershed delineationdelineated watersheds for
each segment
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Watershed source loadings of zinc
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Current watershed sources of zinc

• Total annual loadings of zinc from non point
  source pollution 282 kg
• Volume of the bay 62.26 Mm3
• Annual concentration of Zinc from NPS 4.53 ?g/L
• Mean Measured concentration of zinc in water in
  Nueces bay 42.1 ?g/L

Watershed sources are not the whole picture
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Estimation of Mass of Zinc in Sediments in Nueces
Bay

• 10 cm sediment bed depth and surface area of 74.9
  km2 ?V 7,490,000 m3
• Mass of sediments 1.984 x1010 kg
• Average concentration of zinc in sediments 440
  ppm (mg/kg)
• Total mass of zinc in sediments 8,730 metric
  tons

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Pollution Sources in Nueces Bay

• Total mass of zinc in sediments 8,730 metric
  tons
• Based on 1 kg/day watershed loading it will take
  24,000 years to accumulate this mass
• We must have point sources or legacy sources !!

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Next Steps

• Estimate background levels of zinc in sediments
• Evaluate point sources
• Consider hydraulics between inner harbor and
  Nueces Bay
• Suggestions

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Zinc Monitoring data Zinc in sediments at
station 12960Nueces river North of Viola Basin
126.7 mg/kg
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Zinc Monitoring data in Nueces bay Zinc in
sediments at station 13421
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Zinc Monitoring data in Nueces bay Zinc in
sediments at station 13422
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Zinc Monitoring data in Nueces bay Zinc in
sediments at station 13425
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Zinc Monitoring data Zinc in sediments at
station 13432 ( Inner Harbor Nr nav bridge)
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Zinc Monitoring data Zinc in sediments at
station 13430 ( Inner Harbor in Avery basin)
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Zinc Monitoring data Zinc in sediments and
water at station 13439( Inner Harbor)
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Zinc Monitoring data Zinc in sediments at
station 13432 ( Inner Harbor Nr nav bridge)